Use of battery banks with P&S cameras

I am currently experimenting with using an external power source to reduce the weight of the camera.

I can load 6 AA (rechargable) batteries into a dual "D" battery holder, where 3 AA batteries in parallel now replace the D battery originally intended for the holder. The D batteries in the holder are in series. Output voltage is 2.7 V as expected.

The cameras work OK with two AA batteries in the battery chamber, and also with external power input via the power input socket from a generic power supply @ 3 V.

However there seems to be a problem when batteries are used. I can start up the cameras (A470) in replay mode and load CHDK, so that I can see the battery indicator is at 100%. But switching to a shooting mode invariably results in the lens not being deployed or the dreaded "Change batteries" message. I am currently using simple low voltage jumper leads for the connection, but resistance doesn't seem to be the problem, and it doesn't seem to matter whether I use 2, 4 or 6 batteries.

Any idea what might be going wrong here? Or any other suggestions for extending shooting time with external batteries?

It looks like the camera needs at least 3V on its external input. When you switch to shooting mode, or shoot, or recharge the flash, then the current draw droops your external battery pack's voltage enough that it matters.

I'd guess that's because there is a diode in external input jack circuit to separate it from the internal battery?

What happens if you use your jumper leads to connect your external battery pack to the internal battery compartment terminals?